Key click elimination circuit



Jan 7,, 1922. I T, N l 2,228,119

KEY CLICK ELIMINATISN CIRCUIT Filed Aug. 12, 2338 Osr/l/a for 0- and Preced/hy Stayes.

77'me 7 772m: i?; 2. F2; 5. I 2%; 4

WITNESSES: INVENTOR c7 1 2 T/readare mm Patented Jan. @952 Y mm rarest: OFFICE v means an cues. summaries cmcm'r Theodore r.

Westinghouse mm. Baltimore. Md. anterior to Electric & Manufacturing Company. East Pittsburgh. Pa a corporation oi.

August 1:. 1m. sci-m No. 224,568

' .4 cum (o1. m-sc) This invention relates to systems of radio telegraphy wherein netic energy is periodically interrupted in accordance with telegraph code signals. and more particularly-to an arrangement for preventing undesirable noises accompanying such interruptions.

i A primary object of this invention is to accomplish the keying of radio tters in such is manner as to eliminate the production of thumps. termed "key clicks," which are observable in radio receivers located within the range oi the transmitter.

The interfering hey clicks are caused by a high order of side-baud frequencies produced by the sudden starting and stopping oi oscillations. In order to eliminate the cause. it is necessary to provide some means whereby the oscillations are controlled to start and stop gradually instead of so abruptly.

Another object of I the shape of the means of reactive elements interposed in the keying circuit and arranged in such relationship of electrical values as to form a critically damped oscillatory circuit. A further object of this invention is to control the rate of increase and decrease oi transmitted high frequency currents upon closure and so opening oi the lreying'mechanism.

Other objects and advantages will beapparent from the following description of the invention. defined particularly in the appended claims, and taken inconnection with the accompanying drawing, in which:

Figure 1 shows schematically the keyed stage of a radio telegraphy transmitter incorporating the novel control circuit in accordance with this invention;

v Fig. 2 shows the current characteristic upon closure of the transmitter key:

Fig. 3 shows the current characteristic upon opening of the key; and

Fig. 4 shows the resultant current wave iorm when combining Figs. 2 and 8, representing the complete cycle of closure and opening of the heying mechanism.

Referring to Fig. .1, only the final amplifier stage of the radio-telegraphy transmitter is shown schematically. To simplify the illustration of the operation'oi the keying system, the latter is shown to be applied to the final amplifier stage, the preceding stages and the oscillator be ing indicated by a conventional block diagram. It is to be understood, however, that it may as this invention is to modify the tran oi electromagtratted wave front or well be applied to other-stages; or in some cases.

to the master oscillator stage when the keying v thereof is contemplated... The output of the preceding stages is coupled to the final amplifier stage by means oithe radio frequency transa former i having primary winding 2 and secondary winding 3. One terminaloi' the secondary winding connects with the grid 4 of the power amplifier tube 5. The other terminal of the secondary winding dis connected to the negative lo terminal of the bias potential source, represented here by the battery 8, through a resistor "I, the positive terminal of the battery being connected to the cathode 8 of the power amplifier tube 5. Theradio frequency currents are provided with a lid low impedance return pathvto the cathode 8 through the bypass condenser 9. The output of the tube 5 includes the primary winding ii! of the coupling transformer ii, the two terminals of the secondary winding 52 thereof being con" so I nected to the antenna i3 and ground it. T851386! tively. The anode E5 of the tube 5 connects to one terminal of the primary winding iii, the other terminal thereof being connected by means of conductor It to the positive terminal of the 25 power supply source. schematically represented here by the battery ii, the negative terminal oi which is connected to ground. To complete the cathode circuit of the tube 5 to ground, an inductive reactance i8 is con- 30 nested between cathode 8 and the anode it of the control tube 20, the cathode 2i of tube 26 being connected by means of conductor 22 to one of the contactors 23 of the key 24, the corresponding contact 25 thereof being connected so to the conductor '26. Across the terminals of the battery ll, that is, between groundand conductor it, is connected a relatively large capacity 21. In power supply systems of the rectified alternating-current type, the capacity 21 is usually so incorporated in the form of a filter condenser. The grid circuit of the control tube 20 includes the grid 28 connected to contact 29 of the key 26, the corresponding contactortil thereof being connected to contactor 23 which, as pre- 45 vlously described, connects to the cathode 2! of the tube 2t. Between cathode 2i and the grid 28, there is connected a resistor Si in series with the bias potential source schematically shown as the battery 32.

The various. contacts and contactors of the key 26 are so arranged that upon pressing/the 'key contactor 28 and contact close prior to the successive closing oi contactor 30 and contact 29. Returning to the cathode-anode porso tion of the amplifier tube 6, it is seen that the cathode terminal of the inductance 18 in the cathode return circuit connects also to a resistor 33 in series with a fixed capacity 34 which 5 terminates at the conductor 13, and the other terminal thereof is connected. to a similar resistance-capa'city network comprising resistor 33 and capacity 34'.

The problem of key click elimination in a 10 radio transmitter is primarily the problem of controlling the rate of increase and decrease of the antenna current when the telegraph key is closed and opened. To properly control the fluctuation of current in the antenna circuit 15 necessarily means control of the power to one or more of the vacuum tubes in the radio transmitter. In the circuit of Fig. 1, the power in the vacuum tube 5 is controlled by means of periodic opening and closing of the power sup= 2o. ply circuit to the tube. In other words, the tube 5 represents a load for the power supply source II. In order to obtain the desired result, it is advantageous to utilize a control tube which is the primary means for disrupting the 25 flow of current in the anode-cathode circuit of the amplifier tube 5, and to control the actuation of the control tube 23 in a secondary circuit in which there is a very small amount of current flow in comparison with the one in the 30 primary circuit. The secondary circuit referred to is the grid circuit of the control tube 29, the key 24 effecting initiation of conductivity of the control tubes by means of short circuiting the bias potential of the source 32 whereby the grid 35 28 is'directly connected to the cathode 2i upon closure of the key 24. r

The various supply sources for the anode potential and grid potentials of the tubes may be batteries, as shown here for the purpose of simso plifying the illustration, or rectillers or generators may be employed. The condenser 21 is a necessary part for the proper functioning of the system, and when generators or batteries are used for the power source, it should be incorporated 45 as indicated here. However, when arectifientype power supply is used, the condenser 21 is usually an inherent part of such supplies and may be omitted.

In describing the operation of the system, the 50 circuit functions as follows: When the key 24 is closed, the contactor 23 and contact 25 close slightly before contactor 30 and contact 29 whereby the negative terminal of the battery i? is connected to the cathode 28 of the control tube 20. 65 However, due to the slight time difierence in the closure of the contactor 33 and contact 29, the grid. 28 of the control tube 20 remains at a cutoff value of potential from the battery 32 and non-conductive until the latter contacts close, short-circuiting the grid resistor 3| and the battery 32, whereby the blocking bias of the con--. trol tube is removed. The primary keying circuit to complete a path for the current from the supply I! to the amplifier tube 5, therefore, is 65 actually made inside the tube 20; that is, by its spaced current path, and sparking which would normally occur when disrupting this circuit by a switch is entirely eliminated. Assuming now conductivity of the tube 23, the operating po- 7 tential for the anode I of the tube 5 will not reach maximum value. immediately due to the action of the reactive components in the circuit, namely, the inductance I8, resistors 33 and 33' and condenser 34 and 34'. The gradual rise of 76 this voltage is due to the fact that the values for the reactive components mentioned are so chosen as to form a critically dampedocillatory circuit. 1

After the anode voltage of the tube 5 has reached its normal value and the key 24 is opened, 5 power is removed by opening of the contacts 23 and 25. At this point, the advantages in the operation 01' the system are clearly observable as follows: After the anode voltage reached a steady value, condensers 34 and 34' are both charged with the same potential; that is, the full anode potential, and, therefore, when contactor 23 and contact 25 are separated, it actually opens the cathode return to the negative terminal of the source l1. At the contact points at this instant, however, there is no potential difference and, therefore, no sparking can ocour; The reason for this is that contacts 30 and 29 actually open first, and if the tube 23 is of the mercury or gas-filled type, the bias potentlal will control only the starting of the tube and not its cutoff. The second action which occurs on opening the key 24 is that the energy stored in the circuit, comprising of the inductance l8, resistors 30 and 33 and condensers 3d and 35', is again controlled by the resonant condition of the circuit whereby the anode voltage decreases to zero gradually, as shown in Fig. 3. The net result for the closing and opening cycle of the key 24 is the combination of the two curves of Figs. 2 and 3, as shown in Fig. 4, which is the ideal wave form for eliminating key clicks.

3 In a practical embodiment for keying a transmitter, the following values for the reactive components were found to give good results.

Inductance l8 henries 10 Condenser 34' microfarad .5

' Condenser 34"-. do .15

Resistor 33 "ohms" 1000 Resistor 33 do 2060 The control tube 20 was of the mercury vapor grid-glow type used for industrial control identified as type KU-628.

In operation, the contacts 23 and 25 close first, applying approximately 3000-11011; potential of the source I! to the anode of the control tube 23, which, however, will not break down until contacts 30 and 29 are closed removing the blocking bias from the grid 28. I The anode circuit for the amplifier 'tube is actually closed by the control tube 20, and no sparking at the contacts of the key 2t occur. At the. break, when opening the key 24, contacts 30 and 29 open first, which has no efiect on the tube operation, for once the control tube is ionized," the grid 23 loses controL Therefore, when the key is released and contacts 23 and 25 open, they perform the duty of breaking the circuit. However, no sparking results again, due to the auction of r the condenser 34' in conjunction with the filter capacitor 27, both being fully charged capacities on either side of the contacts 23 and 25. The control tube need not be of the gas-filled type, and 'an ordinary vacuum tube may be employed in its place, in which case, contacts 23 and 25 may be eliminated by a permanent connection between them, and the control of both make and break accomplished by the grid control 0. the contacts so and 29.

What is claimed is:

1. In 'a keying system for radiov telegraph transmitters, a vacuum tube having anode, cathode and at least a control electrode, a power supply for energizing said tube, one terminal 7 means of said supply being eflectively connected to said anode and another terminal thereof to said cathode, whereby said tube forms a load for said supply, a keying circuit interposed between said supply and said tube including means for interrupting the connection to said cathode at a relatively fast rate, and means for controlling the rate of increase of current in said circuit during closure of said first mentioned means and the rate of decrease of said current upon opening thereof, comprising reactive elements in series and parallel relationship with respect to said load interposed in said circuit, said elements being so proportioned as to form a critically damped oscillatory circuit.

2. In a keying system for radio telegraph transmitters, a vacuum tube having anode, cathode and at least a control electrode, a power supply 'for energizing said tube, one terminal thereof being eflectively connected to said anode and another terminal to said cathode whereby said tube forms a load for said supply, a keying circuit interposed between said supply and said tube including means for interrupting the connection to one of said electrodes at a relatively fast rate, and means for controlling the rate of rise of current in said tube during closure of said first mentioned means and the rate of decay of said current upon opening thereof, comprising reactive elements in series and parallel relationship with said load interposed in said circuit, said elements being so proportioned as to form a critically damped oscillatory circuit.

3. In a keying system for radio telegraph transmitters, a vacuum. tube for amplifying high I frequency currents having cathode, anode, and at least one control electrode, a power supply for energizing said tube, one terminal of said supply being eflectively connected to said anode and another terminal thereof to said cathode, a fixed capacity between said terminals, a keying circuit for interrupting the flow of current from said supply to said tube at a relatively fast rate, including a current interrupter, and means for controlling the rate of increase of anode current of said tube during closure of said interrupter and the rate of decrease of said anode current upon opening of said interrupter, comprising an inductance serial-1y interposed between cathode and said other terminal of said supply, a fixed capacity and a resistance in series connected effectively in parallel between cathode and the anode terminal of said supply and another fixed capacity and resistance in series connected effectively in parallel with said supply, said series and parallel elements being so proportioned as to .form an oscillatory circuit critically damped in character.

4. In a keying system for radio telegraph transmitters, a keying circuit and a keyed circult interconnected by means of electrical coupling elements, a source of current so related to said keyed circuit as to ,be periodically interrupted by said keying circuit, said last-mentioned circuit including a control tube having anode, cathode and control electrode, the anode-cathode path of said tube forming a conductive connection between said source and said keyed circult, a current interrupter including a plurality of contactors in said keying circuit, one pair of said contaotors operating to connect said source to said cathode and another pair to connect said grid to a supply of bias potential, whereby upon closure of said contactors said tube is energized to conductively pass current from said source to said keyed circuit, said coupling elements comprising an inductance and capacities and resistive THEODORE P. 1mm. 

